Linear block copolymer and resin composition containing the same

ABSTRACT

Disclosed is a linear block copolymer comprising at least two vinyl aromatic hydrocarbon polymer blocks (S), at least two conjugated diene polymer blocks (B) and at least one vinyl aromatic hydrocarbon/conjugated diene copolymer block (B/S); the linear block copolymer having a specific block configuration wherein both terminal polymer blocks of the linear block copolymer are S blocks, both terminal S blocks have, bonded directly to the respective inner ends thereof, B blocks, and the B blocks, which are bonded directly to the respective inner ends of both terminal polymer blocks (S), have therebetween one or two B/S blocks which is or are bonded directly to the respective inner ends of the polymer blocks (B); the linear block copolymer comprising at least two fractions having different peak molecular weights, and both terminal S blocks in total comprising at least two fractions having different peak molecular weights. Also disclosed is a resin composition comprising the linear block copolymer and a styrene-containing resin in a specific amount ratio.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP99/04159 which has an Internationalfiling date of Aug. 3, 1999, which designated the United States ofAmerica.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a linear block copolymer. Moreparticularly, the present invention is concerned with a linear blockcopolymer comprising at least two vinyl aromatic hydrocarbon polymerblocks (S), at least two conjugated diene polymer blocks (B) and atleast one vinyl aromatic hydrocarbon/conjugated diene copolymer block(B/S); the linear block copolymer having a specific block configurationwherein both terminal polymer blocks of the linear block copolymer are Sblocks, both terminal S blocks have, bonded directly to the respectiveinner ends thereof, B blocks, and the B blocks, which are bondeddirectly to the respective inner ends of both terminal polymer blocks(S), have therebetween one or two B/S blocks which is or are bondeddirectly to the respective inner ends of the polymer blocks (B); thelinear block copolymer comprising at least two fractions havingdifferent peak molecular weights, and both terminal S blocks in totalcomprising at least two fractions having different peak molecularweights. The present invention is also concerned with a resincomposition comprising the linear block copolymer and astyrene-containing resin in a specific amount ratio. By molding thelinear block copolymer of the present invention or the resin compositioncontaining the linear block copolymer, a shaped article retaining hightransparency and having excellent rigidity and excellent impactresistance can be obtained.

2. Prior Art

A block copolymer comprising a vinyl aromatic hydrocarbon and aconjugated diene wherein the vinyl aromatic hydrocarbon content isrelatively high, has various excellent characteristics, such astransparency and impact resistance, so that such a block copolymer isused for producing injection-molded products, extrusion-molded products(such as a sheet and a film) and the like. Conventionally, in an attemptto improve the mechanical properties (such as impact resistance) of ashaped article produced from a block copolymer while retaining thetransparency of the shaped article, there have been proposed not onlyblock copolymers comprising a vinyl aromatic hydrocarbon and aconjugated diene and methods for producing such block copolymers, butalso resin compositions comprising such block copolymers. For example,in an attempt to improve the transparency and impact resistance of ablock copolymer, Unexamined Japanese Patent Application Laid-OpenSpecification No. 52-58788 (corresponding to U.S. Pat. No. 4,167,545)discloses a branched block copolymer obtained by division-wise adding acatalyst to a block copolymerization system. Also, for improving theenvironmental stress cracking resistance of a block copolymer,Unexamined Japanese Patent Application Laid-Open Specification No.4-277509 (corresponding to U.S. Pat. No. 5,227,419 and European PatentNo. 492490) discloses a method for producing a block copolymer havinggradually varied properties, which comprises division-wise adding acatalyst to a block copolymerization system. On the other hand, forobtaining a block copolymer having transparency and mechanicalproperties, Unexamined Japanese Patent Application Laid-OpenSpecification No. 63-145314 (corresponding to U.S. Pat. No. 4,939,208and European Patent No. 270515) discloses a method for producing a blockcopolymer having an S₁-B₁-B/S-S₂ block configuration, wherein S₁ and S₂each represent an aromatic vinyl uniform polymer block, B₁ represents aconjugated diene uniform polymer block, and B/S represents a randomcopolymer block. Further, with a view to improving the transparency andimpact resistance of a block copolymer, Unexamined Japanese PatentApplication Laid-Open Specification No. 7-97418 discloses a blockcopolymer which has characteristic features with respect to the vinylaromatic hydrocarbon block ratio, the arrangement of the polymer blocks,the ratio of the conjugated diene in a segment in which a vinyl aromatichydrocarbon and a conjugated diene are randomly copolymerized, and thelike. However, the above-mentioned conventional block copolymers haveproblems in that when such a block copolymer is formulated into a resincomposition thereof with a styrene-containing resin and molded to obtaina sheet, followed by processing to produce a shaped article, such as acup for beverage or a cup for frozen or cold dessert, the shaped articlehas an unsatisfactory balance of transparency, impact resistance,rigidity and the like. Accordingly, it has been desired to produce ablock copolymer which is improved so that it is capable of producingtherefrom a shaped article having excellent transparency, impactresistance, rigidity and the like.

SUMMARY OF THE INVENTION

In this situation, the present inventors have made extensive andintensive studies with a view to solving the above-mentioned problemsaccompanying the prior art block copolymer. As a result, it hassurprisingly been found that when a specific linear block copolymer issubjected to processing to obtain a shaped article, the article exhibitsa good balance of transparency, rigidity and impact resistance, whereinthe linear block copolymer comprises at least two vinyl aromatichydrocarbon polymer blocks (S), at least two conjugated diene polymerblocks (B) and at least one vinyl aromatic hydrocarbon/conjugated dienecopolymer block (B/S); the linear block copolymer having a specificblock configuration wherein both terminal polymer blocks of the linearblock copolymer are S blocks, both terminal S blocks have, bondeddirectly to the respective inner ends thereof, B blocks, and the Bblocks, which are bonded directly to the respective inner ends of bothterminal polymer blocks (S), have therebetween one or two B/S blockswhich is or are bonded directly to the respective inner ends of thepolymer blocks (B); the linear block copolymer comprising at least twofractions having different peak molecular weights, and both terminal Sblocks in total comprising at least two fractions having different peakmolecular weights. Based on this finding, the present invention has beencompleted.

Accordingly, it is a primary object of the present invention to providea novel linear block copolymer having excellent transparency, impactresistance and rigidity.

It is another object of the present invention to provide a resincomposition comprising the above-mentioned linear block copolymer and astyrene-containing resin, which has excellent transparency, impactresistance and rigidity.

The foregoing and other objects, features and advantages of the presentinvention will be apparent from the following detailed description andappended claims.

DETAILED DESCRIPTION OF THE INVENTION

In a primary aspect of the present invention, there is provided a linearblock copolymer comprising:

at least two vinyl aromatic hydrocarbon polymer blocks (S);

at least two conjugated diene polymer blocks (B); and

at least one vinyl aromatic hydrocarbon/conjugated diene copolymer block(B/S),

the total amount of vinyl aromatic hydrocarbon monomer units in thelinear block copolymer and the total amount of conjugated diene monomerunits in the linear block copolymer being, respectively, from 65 to 90%by weight and from 35 to 10% by weight, based on the weight of thelinear block copolymer,

the linear block copolymer having a block configuration wherein:

both terminal polymer blocks of the linear block copolymer are vinylaromatic hydrocarbon polymer blocks (S),

both terminal vinyl aromatic hydrocarbon polymer blocks (S) have, bondeddirectly to the respective inner ends thereof, conjugated diene polymerblocks (B), and

the conjugated diene polymer blocks (B), which are bonded directly tothe respective inner ends of both terminal vinyl hydrocarbon polymerblocks (S), have therebetween one or two vinyl aromatichydrocarbon/conjugated diene copolymer blocks (B/S) which is or arebonded directly to the respective inner ends of the conjugated dienepolymer blocks (B), wherein, when the polymer blocks (B) havetherebetween two vinyl aromatic hydrocarbon/conjugated diene copolymerblocks (B/S), the two copolymer blocks (B/S) have therebetween at leastone polymer block selected from the group consisting of the polymerblocks (S), (B) and (B/S) in a contiguous relationship,

the linear block copolymer comprising at least two different fractions(α) and (β), wherein the fraction (α) has at least one peak molecularweight in the range of from 50,000 to 150,000 in a first chromatogramtaken by gel permeation chromatography (GPC) with respect to the linearblock copolymer, and the fraction (β) has at least one peak molecularweight in the range of from more than 150,000 to 350,000 in the firstchromatogram,

both terminal vinyl aromatic hydrocarbon polymer blocks (S) in totalcomprising a fraction having at least one peak molecular weight in therange of from 10,000 to 60,000 in a second chromatogram taken by GPCwith respect to both terminal vinyl aromatic hydrocarbon polymer blocks(S), and a fraction having at least one peak molecular weight in therange of from 120,000 to 250,000 in the second chromatogram,

the linear block copolymer having a weight average molecular weight offrom 50,000 to 500,000.

In another aspect of the present invention, there is provided a resincomposition comprising 100 parts by weight of the above-mentioned linearblock copolymer and 30 to 400 parts by weight of a styrene-containingresin.

For easy understanding of the present invention, the essential featuresand various embodiments of the present invention are enumerated below.

1. A linear block copolymer comprising:

at least two vinyl aromatic hydrocarbon polymer blocks (S);

at least two conjugated diene polymer blocks (B); and

at least one vinyl aromatic hydrocarbon/conjugated diene copolymer block(B/S),

the total amount of vinyl aromatic hydrocarbon monomer units in thelinear block copolymer and the total amount of conjugated diene monomerunits in the linear block copolymer being, respectively, from 65 to 90%by weight and from 35 to 10% by weight, based on the weight of thelinear block copolymer,

the linear block copolymer having a block configuration wherein:

both terminal polymer blocks of the linear block copolymer are vinylaromatic hydrocarbon polymer blocks (S),

both terminal vinyl aromatic hydrocarbon polymer blocks (S) have, bondeddirectly to the respective inner ends thereof, conjugated diene polymerblocks (B), and

the conjugated diene polymer blocks (B), which are bonded directly tothe respective inner ends of both terminal vinyl hydrocarbon polymerblocks (S), have therebetween one or two vinyl aromatichydrocarbon/conjugated diene copolymer blocks (B/S) which is or arebonded directly to the respective inner ends of the conjugated dienepolymer blocks (B), wherein, when the polymer blocks (B) havetherebetween two vinyl aromatic hydrocarbon/conjugated diene copolymerblocks (B/S), the two copolymer blocks (B/S) have therebetween at leastone polymer block selected from the group consisting of the polymerblocks (S), (B) and (B/S) in a contiguous relationship,

the linear block copolymer comprising at least two different fractions(α) and (β), wherein the fraction (α) has at least one peak molecularweight in the range of from 50,000 to 150,000 in a first chromatogramtaken by gel permeation chromatography (GPC) with respect to the linearblock copolymer, and the fraction (β) has at least one peak molecularweight in the range of from more than 150,000 to 350,000 in the firstchromatogram,

both terminal vinyl aromatic hydrocarbon polymer blocks (S) in totalcomprising a fraction having at least one peak molecular weight in therange of from 10,000 to 60,000 in a second chromatogram taken by GPCwith respect to both terminal vinyl aromatic hydrocarbon polymer blocks(S), and a fraction having at least one peak molecular weight in therange of from 120,000 to 250,000 in the second chromatogram,

the linear block copolymer having a weight average molecular weight offrom 50,000 to 500,000.

2. The block copolymer according to item 1 above, which has a blockconfiguration represented by the following formula (1):

S-(B-B/S)_(n)-B-S  (1)

wherein each S independently represents the vinyl aromatic hydrocarbonpolymer block;

each B independently represents the conjugated diene polymer block;

the or each B/S represents the vinyl aromatic hydrocarbon/conjugateddiene copolymer block; and

n represents an integer of from 1 to 5.

3. The block copolymer according to item 1 or 2 above, wherein bothterminal vinyl aromatic hydrocarbon polymer blocks (S) in total comprisea fraction having at least one peak molecular weight in the range offrom 10,000 to 50,000 in the second chromatogram, and a fraction havingat least one peak molecular weight in the range of from 150,000 to250,000 in the second chromatogram.

4. The block copolymer according to any one of items 1 to 3 above, whichhas a vinyl aromatic hydrocarbon polymer block ratio of from 60 to 95%by weight, wherein the block ratio is defined as the percent by weightof the vinyl aromatic hydrocarbon monomer units contained in the polymerblocks (S), based on the total weight of vinyl aromatic hydrocarbonmonomer units contained in the linear block copolymer.

5. The block copolymer according to any one of items 1 to 4 above,wherein the fraction (α) has at least one peak molecular weight in therange of from 50,000 to 120,000 in the first chromatogram, and thefraction (β) has at least one peak molecular weight in the range of from160,000 to 300,000 in the first chromatogram.

6. The block copolymer according to any one of items 1 to 5 above,wherein the content of the fraction (α) in the linear block copolymerand the content of the fraction (β) in the linear block copolymer arefrom 30 to 70% by weight and from 70 to 30% by weight, respectively.

7. A resin composition comprising 100 parts by weight of the linearblock copolymer of any one of items 1 to 6 above and 30 to 400 parts byweight of a styrene-containing resin.

Hereinbelow, the present invention is described in detail.

The linear block copolymer of the present invention comprises at leasttwo vinyl aromatic hydrocarbon polymer blocks (S), at least twoconjugated diene polymer blocks (B), and at least one vinyl aromatichydrocarbon/conjugated diene copolymer block (B/S). In the linear blockcopolymer of the present invention, each of the at least two vinylaromatic hydrocarbon polymer blocks (S) generally comprises a pluralityof vinyl aromatic hydrocarbon monomer units. Both terminal polymerblocks of the linear block copolymer, that is, two vinyl aromatichydrocarbon polymer blocks (S), are different from each other; however,when the linear block copolymer contains three or more vinyl aromatichydrocarbon polymer blocks (S), some of these vinyl aromatic hydrocarbonpolymer blocks (S) may be identical. Each of the at least two conjugateddiene polymer blocks (B) generally comprises a plurality of conjugateddiene monomer units. These conjugated diene polymer blocks (B) may beidentical or different. The at least one vinyl aromatichydrocarbon/conjugated diene copolymer block generally comprises vinylaromatic hydrocarbon monomer units and conjugated diene monomer units.When the linear block copolymer contains a plurality of copolymer blocks(B/S), these copolymer blocks (B/S) may be identical or different. It ispossible that, in the course of the polymerization for producing thelinear block copolymer, a very small amount of vinyl aromatichydrocarbon monomer units gets mixed into conjugated diene monomer unitsin polymer block (B), and a very small amount of conjugated dienemonomer units gets mixed into vinyl aromatic hydrocarbon monomer unitsin polymer block (S).

As mentioned above, in the linear block copolymer of the presentinvention, both terminal polymer blocks are vinyl aromatic hydrocarbonpolymer blocks (S). Both terminal vinyl aromatic hydrocarbon polymerblocks (S) have, bonded directly to the respective inner ends thereof,conjugated diene polymer blocks (B). These conjugated diene polymerblocks (B) have therebetween one or two vinyl aromatichydrocarbon/conjugated diene copolymer blocks (B/S) which is or arebonded directly to the respective inner ends of the conjugated dienepolymer blocks, wherein, when the polymer blocks (B) have therebetweentwo vinyl aromatic hydrocarbon/conjugated diene copolymer blocks (B/S),the two copolymer blocks (B/S) have therebetween at least one polymerblock selected from the group consisting of the polymer blocks (S), (B)and (B/S) in a contiguous relationship. It is required that the linearblock copolymer of the present invention have the above-mentioned blockconfiguration.

Further, it is preferred that the linear block copolymer of the presentinvention has a block configuration represented by the following formula(1):

S-(B-B/S)_(n)-B-S  (1)

wherein each S independently represents the vinyl aromatic hydrocarbonpolymer block;

each B independently represents the conjugated diene polymer block;

the or each B/S represents the vinyl aromatic hydrocarbon/conjugateddiene copolymer block; and

n represents an integer of from 1 to 5.

Examples of linear block copolymers having the above-mentioned blockconfiguration of formula (1) include block copolymers respectivelyhaving block configurations represented by the following formulae:

S₁-B₁-B/S-B₂-S₂,

and

S₁-B₁-B/S-B₃-B/S-B₂-S₂,

wherein the suffixes attached to the symbols “S” and “B” respectivelyrepresent the block identification numbers of vinyl aromatic hydrocarbonpolymer blocks (S) and conjugated diene polymer blocks (B) in the linearblock copolymer.

As described below, the linear block copolymers having theabove-mentioned block configurations can be obtained by polymerizing avinyl aromatic hydrocarbon monomer and a conjugated diene monomer in ahydrocarbon solvent in the presence of an organolithium compound used asa polymerization initiator under appropriate conditions.

The linear block copolymer of the present invention comprises at leasttwo different fractions (α) and (β), wherein the fraction (α) has atleast one peak molecular weight in the range of from 50,000 to 150,000,preferably from 50,000 to 120,000, in a first chromatogram taken by gelpermeation chromatography (GPC) with respect to the linear blockcopolymer, and the fraction (β) has at least one peak molecular weightin the range of from more than 150,000 to 350,000, preferably from160,000 to 300,000, in the first chromatogram. When the peak molecularweight of the fraction (α) is less than 50,000 or more than 150,000, orwhen the peak molecular weight of the fraction (β) is less than 150,000or more than 350,000, the impact resistance of the linear blockcopolymer is disadvantageously lowered.

In the present invention, it is preferred that the content of thefraction (α) in the linear block copolymer is from 30 to 70% by weight,more advantageously from 35 to 65% by weight. In the present invention,it is also preferred that the content of the fraction (β) in the linearblock copolymer is from 70 to 30% by weight, more advantageously from 65to 35% by weight.

As examples of methods for producing a linear block copolymer comprisingsuch a plurality of fractions having different peak molecular weights,namely, a linear block copolymer having a bimodal or a multimodalmolecular weight distribution, there can be mentioned the following twomethods. One method consists in that, in the course of thepolymerization reaction of the vinyl aromatic hydrocarbon monomers forforming the terminal blocks of molecular chains on the polymerizationinitiation side, the polymerization initiator and the vinyl aromatichydrocarbon monomers are further added to the polymerization reactionsystem to generate fresh polymerization initiating points for formingfresh additional molecular chains of linear block copolymer, therebyproducing a plurality of fractions having different peak molecularweights. The other method consists in that, in the course of thepolymerization reaction of the vinyl aromatic hydrocarbon monomers forforming the terminal blocks of molecular chains on the polymerizationtermination side, a deactivating agent, such as an alcohol or water, isadded to the polymerization reaction system to deactivate a part of thepolymerization initiator, thereby terminating the polymerizationreaction of a part of molecular chains, and then the vinyl aromatichydrocarbon monomers are again added to the polymerization reactionsystem to continue the polymerization reaction of the remaining part ofmolecular chains for forming fresh additional terminal blocks of linearblock copolymer on the polymerization termination side, therebyproducing a plurality of fractions having different peak molecularweights. These methods can be employed individually or in combination.By these methods, fractions having different peak molecular weights canbe obtained in a single reaction system. Such a linear block copolymerhaving fractions having different peak molecular weights canalternatively be obtained by mixing together linear block copolymershaving different peak molecular weights which have been separatelyprepared. The thus obtained linear block copolymer comprises fraction(α) having a low content of vinyl aromatic hydrocarbon monomer units andfraction (β) having a high content of vinyl aromatic hydrocarbon monomerunits. Elucidation has not been made as to the reason why the linearblock copolymer of the present invention, which has a good balance oftransparency, rigidity and impact resistance, can be obtained by thebimodalization or multimodalization of the molecular weight distributionof a linear block copolymer comprising a vinyl aromatic hydrocarbon anda conjugated diene and having a relatively high vinyl aromatichydrocarbon content. However, it is considered that the coexistence, inthe linear block copolymer, of the elastomeric fraction (α), which has alow content of vinyl aromatic hydrocarbon monomer units, and theresinous fraction (β), which has a high content of vinyl aromatichydrocarbon monomer units, enables such a block copolymer to exhibitexcellent mechanical properties, while retaining the transparency whichis inherent in this type of block copolymer comprising vinyl aromatichydrocarbon polymer blocks and conjugated diene polymer blocks.

In the present invention, the peak molecular weight of the linear blockcopolymer can be determined by GPC. Specifically, the peak molecularweight of the linear block copolymer can be determined by a method whichcomprises subjecting the linear block copolymer to GPC to obtain a GPCchromatogram (first chromatogram) of the linear block copolymer, anddetermining the peak molecular weight of the linear block copolymer bythe conventional method using a calibration curve obtained from GPCchromatograms showing the peak molecular weights of monodispersepolystyrene samples (see, for example, Gel Permeation Chromatography,pp. 81-85, 1976, published by Maruzen Co., Ltd., Japan). The content ofeach of the fractions in the linear block copolymer can be calculatedfrom the ratio of the area of each of the peaks in the GPC chromatogramof the linear block copolymer.

With respect to the linear block copolymer of the present invention,both terminal vinyl aromatic hydrocarbon polymer blocks (S) in totalcomprise a fraction having at least one peak molecular weight in therange of from 10,000 to 60,000, preferably from 10,000 to 50,000, in achromatogram (second chromatogram) taken by GPC with respect to bothterminal vinyl aromatic hydrocarbon polymer blocks (S), and a fractionhaving at least one peak molecular weight in the range of from 120,000to 250,000, preferably from 150,000 to 250,000, in the secondchromatogram. The peak molecular weights of both terminal vinyl aromatichydrocarbon polymer blocks can be controlled by varying the amount of acatalyst used in the production of both terminal vinyl aromatichydrocarbon polymer blocks (S), the amount of the vinyl aromatichydrocarbon added in the course of the polymerization reaction for theterminal vinyl aromatic hydrocarbon polymer blocks (S), and the like.When the peak molecular weight of the fraction on the side of the lowmolecular weight is less than 10,000 or more than 60,000, or when thepeak molecular weight of the fraction on the side of the high molecularweight is less than 120,000 or more than 250,000, the impact resistanceof the linear block copolymer is disadvantageously lowered. The methodfor determining the peak molecular weight of both terminal vinylaromatic hydrocarbon polymer blocks will be described below.

In the linear block copolymer of the present invention, the total amountof vinyl aromatic hydrocarbon monomer units and the total amount ofconjugated diene monomer units are, respectively, from 65 to 90% byweight and from 35 to 10% by weight, based on the weight of the linearblock copolymer. It is preferred that the total amount of vinyl aromatichydrocarbon monomer units in the linear block copolymer and the totalamount of conjugated diene monomer units in the linear block copolymerare, respectively, from 70 to 85% by weight and from 30 to 15% byweight, based on the weight of the linear block copolymer. When thetotal amount of vinyl aromatic hydrocarbon monomer units in the linearblock copolymer and the total amount of conjugated diene monomer unitsin the linear block copolymer are, respectively, less than 65% by weightand more than 35% by weight, based on the weight of the linear blockcopolymer, the rigidity of the linear block copolymer isdisadvantageously lowered. On the other hand, when the total amount ofvinyl aromatic hydrocarbon monomer units in the linear block copolymerand the total amount of conjugated diene monomer units in the linearblock copolymer are, respectively, more than 90% by weight and less than10% by weight, based on the weight of the linear block copolymer, theimpact resistance of the linear block copolymer is disadvantageouslylowered.

Examples of vinyl aromatic hydrocarbon monomers used in the presentinvention include styrene, o-methylstyrene, p-methylstyrene,p-tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene,vinylnaphthalene, vinylanthracene and 1,1-diphenylethylene. Of these,styrene is especially preferred. These vinyl aromatic hydrocarbonmonomers can be used individually or in combination. In the presentinvention, a conjugated diene means a diolefin having a pair ofconjugated double bonds. Examples of conjugated dienes used in thepresent invention include 1,3-butadiene, 2-methyl-1,3-butadiene(isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene and1,3-hexadiene. Of these, 1,3-butadiene and isoprene are especiallypreferred. These conjugated dienes can be used individually or incombination.

It is preferred that the linear block copolymer of the present inventionhas a vinyl aromatic hydrocarbon polymer block ratio (hereinafter,frequently referred to simply as an “S block ratio”) of from 60 to 95%by weight, more advantageously from 65 to 90% by weight, wherein the Sblock ratio is defined as the percent by weight of the vinyl aromatichydrocarbon monomers contained in polymer blocks (S), based on the totalweight of all vinyl aromatic hydrocarbon monomers contained in thelinear block copolymer. In the present invention, the S block ratio isobtained as follows. The linear block copolymer is subjected tooxidative degradation (of the conjugated diene components) using t-butylhydroperoxide in the presence of osmium tetraoxide as a catalyst toobtain the vinyl aromatic hydrocarbon polymer block components (exceptthose having an average degree of polymerization of about 30 or less),and the ratio of the weight of the vinyl aromatic hydrocarbon polymerblock components to the total weight of all vinyl aromatic hydrocarbonmonomers contained in the linear block copolymer is obtained in terms ofthe percent by weight (see the method described in I. M. Kolthoff etal., J. Polym. Sci. vol. 1, No. 5, pp. 429-433, 1946).

In the linear block copolymer of the present invention, the block ratiocan be controlled by varying the weights of vinyl aromatic hydrocarbonmonomers and conjugated diene monomers contained in vinyl aromatichydrocarbon/conjugated diene copolymer blocks (B/S), the weight ratiothereof, the polymerization reactivity ratio thereof, and the like.Illustratively stated, the block ratio can be controlled by a methodwhich comprises polymerizing vinyl aromatic hydrocarbon monomers andconjugated diene monomers while continuously adding a mixture thereof tothe polymerization reaction system, or by a method which comprisescopolymerizing vinyl aromatic hydrocarbon monomers and conjugated dienemonomers using a polar compound which acts as a randomizing agent. Thesemethods can be employed individually or in combination.

Examples of polar compounds used as a randomizing agent in the presentinvention include ethers, such as tetrahydrofuran, diethylene glycoldimethyl ether and diethylene glycol dibutyl ether; amines, such astriethylamine and tetramethylethylenediamine; thioethers; phosphines;phosphoramides; alkylbenzenesulfonates; and potassium and sodiumalkoxides.

The peak molecular weights of both terminal vinyl aromatic hydrocarbonpolymer blocks of the linear block copolymer of the present inventioncan be determined by substantially the same method as employed fordetermining the peak molecular weight of the linear block copolymermentioned above, that is, the method which comprises subjecting to GPCthe above-mentioned vinyl aromatic hydrocarbon polymer block componentswhich have been obtained, in the measurement of the S block ratio, bythe oxidative degradation of the linear block copolymer.

The linear block copolymer of the present invention has a weight averagemolecular weight of from 50,000 to 500,000. The weight average molecularweight of the linear block copolymer can be determined by GPC usingstandard polystyrene samples.

From the viewpoint of the processability by molding, it is preferredthat the melt flow rate (MFR) of the linear block copolymer of thepresent invention is from 0.1 to 50 g/10 min, more advantageously from 1to 20 g/10 min, wherein the MFR is measured in accordance with JISK-6870under condition G (temperature: 200° C., load: 5 kg).

The linear block copolymer of the present invention can be produced byconventional methods, such as a method described in U.S. Pat. No.4,939,208, which comprise successively polymerizing vinyl aromatichydrocarbon monomers and/or conjugated diene monomers in a hydrocarbonsolvent in the presence of an organolithium compound as a polymerizationinitiator so that a linear block copolymer having the above-mentionedblock configuration can be obtained. As a representative example of suchmethods, there can be mentioned a method for producing a linear blockcopolymer in a hydrocarbon solvent in the presence of an organolithiumcompound as a polymerization initiator, which comprises the steps: (1)initiating the polymerization of vinyl aromatic hydrocarbon monomers ina polymerization reaction system to produce vinyl aromatic hydrocarbonpolymer block (S₁); (2) after the production of S₁ block, feedingconjugated diene monomers to the reaction system to produce conjugateddiene polymer block (B₁) which is bonded directly to S₁ block; (3) afterthe production of B₁ block, continuously feeding a mixture of vinylaromatic hydrocarbon monomers and conjugated diene monomers to thereaction system to produce vinyl aromatic hydrocarbon/conjugated dienecopolymer block (B/S) which is bonded directly to B₁ block; (4) afterthe production of B/S block, feeding conjugated diene monomers to thereaction system to produce conjugated diene polymer block (B₂) which isbonded directly to B/S block; (5) after the production of B₂ block,feeding vinyl aromatic hydrocarbon monomers to the reaction system toproduce vinyl aromatic hydrocarbon polymer block (S₂) which is bondeddirectly to B₂ block; and (6) after the polymerization of the vinylaromatic hydrocarbon monomers in step (5) above, adding a deactivatingagent to the reaction system to deactivate the organolithium compound,thereby producing a linear block copolymer. In the production of thelinear block copolymer, it is preferred that the polymerizationreactions are performed at a temperature of from −20 to 150° C. under apressure sufficient to maintain the polymerization reaction system in aliquid state. (In the above, the suffixes attached to the symbols “S”and “B” respectively represent the block identification numbers of vinylaromatic hydrocarbon polymer blocks (S) and conjugated diene polymerblocks (B) in the linear block copolymer.)

With respect to the method for producing the linear block copolymer ofthe present invention, which has a bimodal or a multimodal molecularweight distribution, There can be mentioned methods which are obtainedby modifying the above-mentioned method. Examples of such methodsinclude a method in which the polymerization initiator and vinylaromatic hydrocarbon monomers are further added to the reaction systemin the course of step (1) of the above-mentioned method to generatefresh polymerization initiating points for forming fresh additionalmolecular chains of linear block copolymer, thereby producing aplurality of fractions having different peak molecular weights, and amethod in which a deactivating agent, such as an alcohol or water, isadded to the reaction system in the course of step (5) of theabove-mentioned method to deactivate a part of the polymerizationinitiator (the organolithium compound), thereby terminating thepolymerization reaction of a part of molecular chains, followed byfurther adding vinyl aromatic hydrocarbon monomers to the reactionsystem to continue the polymerization reaction of the remaining part ofmolecular chains for forming fresh additional blocks of linear blockcopolymer, thereby producing a plurality of fractions having differentpeak molecular weights. These methods can be employed individually or incombination. By the above-mentioned method, fractions having differentpeak molecular weights can be obtained in a single reaction system. Thelinear block copolymer of the present invention, which has a bimodal ormultimodal molecular weight distribution, can also be obtained, forexample, by a method in which linear block copolymers having differentpeak molecular weights are separately produced by the above-mentionedmethod or the like, and these linear block copolymers are mixedtogether.

Examples of hydrocarbon solvents used for producing the linear blockcopolymer of the present invention include aliphatic hydrocarbons, suchas butane, pentane, hexane, isopentane, heptane, octane and isooctane;alicyclic hydrocarbons, such as cyclopentane, methylcyclopentane,cyclohexane, methylcyclohexane and ethylcyclohaxane; and aromatichydrocarbons, such as benzene, toluene, ethylbenzene and xylene.

The resin composition of the present invention can be produced byblending a styrene-containing resin in an amount of from 30 to 400 partsby weight, preferably from 50 to 300 parts by weight, with 100 parts byweight of the above-mentioned linear block copolymer. When the amount ofthe styrene-containing resin is less than 30 parts by weight, relativeto 100 parts by weight of the linear block copolymer, the rigidity ofthe resin composition is unsatisfactory. When the amount of thestyrene-containing resin is more than 400 parts by weight, relative to100 parts by weight of the linear block copolymer, the impact resistanceof the resin composition is disadvantageously lowered.

As a styrene-containing resin used in the present invention, there canbe mentioned a non-rubber-modified, styrene-containing polymer. Arubber-modified polystyrene may also be used as long as the resincomposition retains transparency. Examples of non-rubber-modifiedstyrene-containing polymers include polystyrene, astyrene-α-methylstyrene copolymer, an acrylonitrilestyrene copolymer, astyrene-(meth)acrylate copolymer and a styrene-maleic anhydridecopolymer. Of these, polystyrene and a styrene-n-butyl acrylatecopolymer are especially preferred. These polymers can be usedindividually or in combination.

The resin composition of the present invention can be produced by anyconventional method. Examples of such methods include a melt-kneadingmethod using a mixing machine generally used in the art, such as an openroll, an intensive mixer, an internal mixer, Kokneader, a continuouskneader having a twin-rotor, or an extruder, and a method whichcomprises dissolving or dispersing each component in a solvent andremoving the solvent from the resultant mixture by heating.

If desired, any additive can be added to the linear block copolymer ofthe present invention and the resin composition containing the same.With respect to the type of additive and the amount of the additive,there is no particular limitation as long as an additive conventionallyused for preparing a plastic is used in an amount conventionally used.Examples of additives include inorganic reinforcing agents, such asglass fiber, glass bead, silica, calcium carbonate and talc; organicreinforcing agents, such as organic fiber, a coumarone-indene resin;crosslinking agents, such as an organic peroxide and an inorganicperoxide; pigments, such as titanium white, carbon black and iron oxide;dyes; flame retardants; antioxidants; ultraviolet light absorbers;antistatic agents; lubricants; plasticizers; other bulk fillers; andmixtures thereof.

The linear block copolymer of the present invention and the resincomposition containing the same can be molded by substantially the samemolding method as employed in the molding of an ordinary thermoplasticresin, wherein the linear block copolymer and/or the resin compositionmay be subjected to coloring treatment. By such a molding method, ashaped article for use in various application fields can be produced.For example, a shaped article produced by a molding method, such asinjection molding or blow molding, can be used as a container for partsof office automation apparatuses, daily necessities, food, miscellaneouscommodities, parts of light electrical appliances and the like. Further,a shaped article (such as a sheet or a film) produced by extrusionmolding is commercially very useful. When such an extruded product isfurther subjected to deep draw forming, such as vacuum forming orpressure forming, a shaped article can be produced which can beadvantageously used in various application fields, such as a containerfor food and a container for vegetables and fruits or confectionery.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be described in more detail withreference to the following Examples and Comparative Examples, whichshould not be construed as limiting the scope of the present invention.

In the Examples and Comparative Examples, the measurement, analysis andevaluation were conducted by the following methods.

(1) Melt flow rate (MFR)

The MFR (g/10 min) is measured in accordance with JIS K-6870 undercondition G (temperature: 200° C., load: 5 kg).

(2) Peak molecular weights and weight average molecular weight of alinear block copolymer, and contents of fractions in the linear blockcopolymer

10 mg of a linear block copolymer is dissolved in 10 mg oftetrahydrofuran (THF) to prepare a solution. The prepared solution issubjected to GPC to obtain a GPC chromatogram. From the obtained GPCchromatogram, the peak molecular weights of fractions in the linearblock copolymer are determined using a calibration curve obtained withrespect to monodisperse polystyrene samples. The contents (% by weight)of fractions in the linear block copolymer are determined from the arearatios of fractions in the GPC chromatogram. Further, the weight averagemolecular weight of the linear block copolymer is determined. Theconditions for GPC analysis conducted above are as follows.

Column: Polystyrene gel

Column temperature: 42° C.

Solvent: THF

Flow rate: 2 ml/min

Detector: RI

(3) S block ratio

30 to 50 mg of a linear block copolymer is accurately weighed and addedto about 10 ml of chloroform. To the resultant mixture are added osmiumtetraoxide and t-butyl hydroperoxide, followed by boiling at 100° C. for20 minutes. To the resultant mixture is added 200 ml of methanol toprecipitate decomposed products. The obtained precipitate is filteredoff using a glass filter (11G4, capacity: 11 ml, maximum pore size: 5 to10 μm) to obtain a filtration residue (block styrenes). The obtainedfiltration residue is weighed. The S block ratio (% by weight) iscalculated from the following formula.

 S block ratio (% by weight)={(the weight (mg) of the filtration residue(block styrene))/(the total weight (mg) of all styrene monomers in thelinear block copolymer)}×100

(4) Peak molecular weight of a styrene block

The peak molecular weights of fractions in styrene polymer blocks aredetermined in substantially the same manner as in item (2) above exceptthat, instead of 10 mg of the linear block copolymer of item (2) above,the filtration residue (block styrenes) obtained in item (3) above isdissolved in THF.

(5) Rigidity

The modulus in tension (kg/cm²) of a sheet produced from a linear blockcopolymer by molding is measured in the machine direction (MD) (in anextrusion direction of the sheet) and in the transverse direction (TD)(in a direction perpendicular to the extrusion direction of the sheet)in accordance with JIS K-6872. The average value of the two valuesobtained with respect to the MD and the TD is used as an index for therigidity of the sheet.

(6) Transparency

The surface of a sheet is coated with liquid paraffin and the haze (%)of the sheet is measured in accordance with ASTM D1003. The smaller thevalue of the haze of the sheet, the higher the transparency of thesheet.

(7) Impact resistance

Pressure forming of a sheet is conducted using a pressure formingmachine (VPF3030, manufactured and sold by United Mold, Japan) toproduce a cup having an opening diameter of 8 cm, a bottom diameter of 5cm and a height of 11 cm. Holding the produced cup around its peripheryjust below the opening (mouth portion for drinking, which is formed byfolding-down), the cup is crushed in a moment in the MD or the TD. Theimpact resistance of the sheet is evaluated by determining whether ornot the cup is caused to have a crack. Six cups produced by the pressureforming are used as test samples for the evaluation of the impactresistance of the sheet; three cups of the six cups are crushed in theMD and the other three cups are crushed in the TD. The criteria for theevaluation are as follows.

◯: no cup is caused to have a crack in the MD or the TD.

×: at least one cup is caused to have a crack in the MD or at least onecup is caused to have a crack in the TD.

EXAMPLE 1

The polymerization reactions for producing a linear block copolymer weresuccessively performed as follows. A 25% by weight solution of styrenein cyclohexane, which contains 20 parts by weight of styrene, wascharged into a 30-liter sealed reactor having a jacket. Into the reactorwere charged 0.08 part by weight of n-butyllithium and 0.015 part byweight of tetramethylethylenediamine. The reactor was purged withnitrogen gas. Then, a first polymerization reaction was performed at 80°C. for 20 minutes while maintaining the pressure in the reactor in therange of from 3 to 5 kgf/cm²G. Then, a 25% by weight solution of1,3-butadiene in cyclohexane, which contains 8 parts by weight of1,3-butadiene, was charged at a time into the reactor to perform asecond polymerization reaction at 80° C. for 15 minutes. Then, a thirdpolymerization reaction was performed at 80° C. while continuouslycharging over 30 minutes into the reactor a 25% by weight solution of1,3-butadiene and styrene in cyclohexane, which contains 9 parts byweight of 1,3-butadiene and 15 parts by weight of styrene. Then, a 25%by weight solution of 1,3-butadiene in cyclohexane, which contains 8parts by weight of 1,3-butadiene, was charged at a time into the reactorto perform a fourth polymerization reaction at 80° C. for 15 minutes.Then, a 25% by weight solution of styrene in cyclohexane, which contains3 parts by weight of styrene, was charged into the reactor to perform afifth polymerization reaction at 80° C. for 5 minutes. Thereafter,methanol was fed to the reactor in a molar amount of 0.4 times the molaramount of the n-butyllithium used, and the reactor was maintained for 5minutes while stirring. Then, a 25% by weight solution of styrene incyclohexane, which contains 37 parts by weight of styrene, was chargedinto the reactor to perform a sixth polymerization reaction at 80° C.for 25 minutes. Thereafter, in order to completely terminate thepolymerization reactions, methanol was fed to the reactor in a molaramount of 0.6 times the molar amount of the n-butyllithium used, and thereactor was stirred for several minutes (1 to 5 minutes). After stirringfor several minutes,2-[1-(2-hydroxy-3,5-di-t-pentylphenyl)ethyl]-4,6-di-t-pentylphenylacrylate as a stabilizer was charged into the reactor in an amount of0.3 part by weight, relative to 100 parts by weight of the producedlinear block copolymer. Then, the cyclohexane solvent was removed fromthe reactor using a double drum dryer to thereby recover the producedlinear block copolymer. Various physical properties of the producedlinear block copolymer were measured by the above-mentioned measuringmethods. These results are shown in Table 1.

As shown in Table 1, the contents of styrene and butadiene in theproduced linear block copolymer are 75% by weight and 25% by weight,respectively, and the produced linear block copolymer is a linear blockcopolymer having an S₁-B₁-B/S-B₂-S₂ block configuration and a bimodalmolecular weight distribution.

Next, 150 parts by weight of general-purpose polystyrene (weight averagemolecular weight: 240,000) were blended with 100 parts by weight of theabove-produced linear block copolymer to obtain a resin composition. Theobtained resin composition was subjected to extrusion molding using a 40mm sheet extruder (USV 40 mm extruder, Union Plastics, Japan) to obtaina sheet having a thickness of 1.2 mm. The rigidity, transparency andimpact resistance of the obtained sheet were evaluated by theabove-mentioned measuring methods. These results are also shown in Table1.

Table 1 shows that the linear block copolymer and the resin compositioncomprising the linear block copolymer and a styrene-containing resinexhibit excellent rigidity, transparency and impact resistance.

EXAMPLES 2 TO 6 AND COMPARATIVE EXAMPLES 1 TO 4

Using styrene and butadiene in amounts (weight ratio) described in Table1, polymerization reactions were successively performed in substantiallythe same manner as in Example 1 to produce a linear block copolymerhaving a block configuration described in Table 1. The contents ofstyrene and butadiene in the produced linear block copolymer werecontrolled by varying the ratio of the weight of styrene to the weightof butadiene. The peak molecular weights of the produced linear blockcopolymer were controlled by varying the amount of n-butyllithium(polymerization initiator) and varying the timing for the addition ofmethanol (deactivating agent) and the amount of methanol. The S blockratio was controlled by varying the ratio of the weight of B/S block inthe linear block copolymer to the weight of the linear block copolymer,wherein when the linear block copolymer has two or more B/S blocks, theweight of B/S block means the total weight of all B/S blocks. The peakmolecular weights of styrene blocks in the linear block copolymer werecontrolled by varying the ratio of the total weight of all S blocks inthe linear block copolymer to the weight of the linear block copolymerand varying the timing for the addition of methanol (deactivating agent)and the amount of methanol.

Next, in accordance with the formulations described in Table 1, thelinear block copolymer was blended with general-purpose polystyrene andstyrene-n-butyl acrylate copolymer to obtain a resin composition. Theobtained resin composition was subjected to extrusion molding insubstantially the same manner as in Example 1 to obtain a sheet. Therigidity, transparency and impact resistance of the obtained sheet wereevaluated by the above-mentioned methods. These results are shown inTable 1.

With respect to the styrene-n-butyl acrylate copolymer used in Examples5 and 6, the content of n-butyl acrylate in the copolymer was 14% byweight, and the MFR (temperature: 200° C., load: 5 kg) of the copolymerwas 2.0 g/10 min.

TABLE 1 Example Example Example Example Example Example ComparativeComparative Comparative Comparative 1 2 3 4 5 6 Example 1 Example 2Example 3 Example 4 Characteristics Block configuration S₁-B₁-B/S-S₁-B₁-B/S- S₁-B₁-B/S- S₁-B₁-B/S- S₁-B₁-B/S- S₁-B₁-B/S- S₁-B₁-B/S-S₁-B₁-B/S- S₁-B₁-B/S- S₁-B₁-B/S- of the structure B₂-S₂ B₂-S₂ B₂-S₂B₂-B/S- B₂-S₂ B₂-S₂ B₂-S₂ B₂-S₂ B₂-S₂ S₂ of linear block B₃-S₂ copolymerAmounts of styrene and 20-8-9/15- 19-7-8/13- 15-12-8/13- 20-3-5/11-20-8-9/15- 20-8-9/15- 20-15-10/9- 27-8-9/14- 15-8-9/12- 23-13-11/13-butadiene (weight ratio) 8-40 7-46 12-40 2-5/11-3-40 8-40 8-40 15-318-34 8-48 40 Styrene content 75 78 68 82 75 75 60 75 75 76 (% by weight)Butadiene content 25 22 32 18 25 25 40 25 25 24 (% by weight) MFR (g/10min) 8 9 4 10 8 8 5 4 5 7 Linear block copolymer Fraction (α) Peakmolecular weight 9.0 8.5 7.0 9.6 9.0 9.0 7.4 12.2 14.2 8.3 (× 10⁴)Content (% by weight) 45 40 42 60 45 45 50 35 100 52 Fraction (β) Peakmolecular weight 20.0 22.0 28.6 17.8 20.0 20.0 19.2 19.8 — 21.3 (× 10⁴)Content (% by weight) 55 60 58 40 55 55 50 65 0 48 Weight averagemolecular 13.1 13.4 15.6 12.5 13.1 13.1 14.2 13.8 14.0 12.9 weight (×10⁴) S block ratio (% by weight) 82 88 84 74 82 82 88 85 87 86 Styreneblocks {circle around (1)} Fraction Peak molecular weight 2.0 2.1 1.63.2 2.0 2.0 3.1 4.1 2.2 3.8 (× 10⁴) {circle around (2)} Fraction Peakmolecular weight 16.0 18.4 18.1 14.3 16.0 16.0 14.6 10.2 8.2 15.3 (×10⁴) Weight Ratio Block copolymer 100 100 100 100 100 100 100 100 100100 (parts by General-purpose 150 100 200 60 0 70 150 150 150 150weight) polystyrene Styrene-n-butyl acrylate 0 0 0 0 150 30 0 0 0 0copolymer Physical Rigidity: modulus in 14,000 13,200 13,300 13,00013,600 13,700 10,200 14,800 15,000 14,500 properties tension (kg/cm²)Transparency:haze (%) 1.3 1.2 2.8 1.1 0.4 1.1 6.2 1.6 1.9 1.5 Impactresistance ◯ ◯ ◯ ◯ ◯ ◯ ◯ X X X

INDUSTRIAL APPLICABILITY

A shaped article obtained by molding the linear block copolymer of thepresent invention or by molding a resin composition which is obtained byblending the linear block copolymer with a styrene-containing resin,such as polystyrene or a styrene-n-butyl acrylate copolymer, not onlyexhibits excellent impact resistance and rigidity but also retains hightransparency, so that such a shaped article can be advantageously usedin various application fields, such as deep draw formed plastic products(e.g., a cup for frozen or cold dessert and a cup for beverage),see-through cases for food through which the contents of the cases canbe clearly seen, materials for wrapping, and blisters.

What is claimed is:
 1. A linear block copolymer comprising: at least twovinyl aromatic hydrocarbon polymer blocks (S); at least two conjugateddiene polymer blocks (B); and at least one vinyl aromatichydrocarbon/conjugated diene copolymer block (B/S), the total amount ofvinyl aromatic hydrocarbon monomer units in said linear block copolymerand the total amount of conjugated diene monomer units in said linearblock copolymer being, respectively, from 65 to 90% by weight and from35 to 10% by weight, based on the weight of said linear block copolymer,said linear block copolymer having a block configuration wherein: bothterminal polymer blocks of said linear block copolymer are vinylaromatic hydrocarbon polymer blocks (S), said both terminal vinylaromatic hydrocarbon polymer blocks (S) have, bonded directly to therespective inner ends thereof, conjugated diene polymer blocks (B), andsaid conjugated diene polymer blocks (B), which are bonded directly tothe respective inner ends of said both terminal vinyl hydrocarbonpolymer blocks (S), have therebetween one or two vinyl aromatichydrocarbon/conjugated diene copolymer blocks (B/S) which is or arebonded directly to the respective inner ends of the conjugated dienepolymer blocks (B), wherein, when said polymer blocks (B) havetherebetween two vinyl aromatic hydrocarbon/conjugated diene copolymerblocks (B/S), said two copolymer blocks (B/S) have therebetween at leastone polymer block selected from the group consisting of said polymerblocks (S), (B) and (B/S) in a contiguous relationship, said linearblock copolymer comprising at least two different fractions (α) and (β),wherein said fraction (α) has at least one peak molecular weight in therange of from 50,000 to 150,000 in a first chromatogram taken by gelpermeation chromatography (GPC) with respect to said linear blockcopolymer, and said fraction (β) has at least one peak molecular weightin the range of from more than 150,000 to 350,000 in said firstchromatogram, said both terminal vinyl aromatic hydrocarbon polymerblocks (S) in total comprising a fraction having at least one peakmolecular weight in the range of from 10,000 to 60,000 in a secondchromatogram taken by GPC with respect to said both terminal vinylaromatic hydrocarbon polymer blocks (S), and a fraction having at leastone peak molecular weight in the range of from 120,000 to 250,000 insaid second chromatogram, said linear block copolymer having a weightaverage molecular weight of from 50,000 to 500,000.
 2. The blockcopolymer according to claim 1, which has a block configurationrepresented by the following formula (1): S-(B-B/S)_(n)-B-S  (1) whereineach S independently represents said vinyl aromatic hydrocarbon polymerblock; each B independently represents said conjugated diene polymerblock; the or each B/S represents said vinyl aromatichydrocarbon/conjugated diene copolymer block; and n represents aninteger of from 1 to
 5. 3. The block copolymer according to claim 1 or2, wherein said both terminal vinyl aromatic hydrocarbon polymer blocks(S) in total comprise a fraction having at least one peak molecularweight in the range of from 10,000 to 50,000 in said secondchromatogram, and a fraction having at least one peak molecular weightin the range of from 150,000 to 250,000 in said second chromatogram. 4.The block copolymer according to claim 1 or 2, which has a vinylaromatic hydrocarbon polymer block ratio of from 60 to 95% by weight,wherein said block ratio is defined as the percent by weight of thevinyl aromatic hydrocarbon monomer units contained in said polymerblocks (S), based on the total weight of vinyl aromatic hydrocarbonmonomer units contained in said linear block copolymer.
 5. The blockcopolymer according to claim 1 or 2, wherein said fraction (α) has atleast one peak molecular weight in the range of from 50,000 to 120,000in said first chromatogram, and said fraction (β) has at least one peakmolecular weight in the range of from 160,000 to 300,000 in said firstchromatogram.
 6. The block copolymer according to claim 1 or 2, whereinthe content of said fraction (α) in said linear block copolymer and thecontent of said fraction (β) in said linear block copolymer are from 30to 70% by weight and from 70 to 30% by weight, respectively.
 7. A resincomposition comprising 100 parts by weight of the linear block copolymerof claim 1 or 2 and 30 to 400 parts by weight of a styrene-containingresin.